Radar transmit bandwidth augmentation

Abstract

Various technologies pertaining to forming a very high instantaneous bandwidth (IBW) radar signal based upon several radio frequency (RF) signals that have sub-bands of the frequency band of the radar signal are described herein. A radar system is configured to address local oscillator leakage across multiple transmit channels of the radar system, such that the radar signal has a relatively constant or other desired amplitude and phase across frequencies of the radar signal. In addition, the radar system is configured to compute a correction signal that pre-distorts each of the sub-frequency channels such that upon combining enables the generation of desired amplitude and phase response across a transmitted pulse.

The invention claimed is: 
     
       1. A radar system configured to emit a very high instantaneous bandwidth radar signal, where the radar signal has a frequency band, the radar system comprising:
 a first transmit channel, where the first transmit channel comprises a first mixer configured to output a first analog radio frequency (RF) signal having a first RF band based upon:
 a first local oscillator (LO) adapted to generate a LO first frequency; and 
 a first digital signal generated by at least one digital signal generator; and 
 
 a second transmit channel, where the second transmit channel comprises a second mixer that outputs a second analog RF signal having a second RF band based upon:
 a second LO adapted to generate a second LO frequency different from the first LO frequency; and 
 a second digital signal generated by the at least one digital signal generator; 
 
 wherein the at least one digital signal generator is adapted to control the amplitudes and shifts phases of the first digital signal and the second digital signal based upon a computed system LO leakage; 
 wherein the amplitudes and phases of the first digital signal and the second digital signal are shifted to address leakage of the first LO and the second LO across transmit channels of the radar system; 
 wherein the radar signal is based upon the first analog RF signal and the second analog RF signal, wherein the frequency band of the radar signal includes the first RF band and the second RF band; 
 wherein the at least one digital signal generator includes a first digital signal generator and a second digital signal generator; 
 wherein the first transmit channel includes the first digital signal generator and the second transmit channel includes the second digital signal generator; 
 wherein the first digital signal generator is adapted to generate the first digital signal and the second digital signal generator is adapted to generate the second digital signal; 
 wherein the computed system LO leakage is computed by a processor, wherein the processor is configured to perform acts comprising:
 causing the first digital signal generator or the second digital signal generator to be deactivated; 
 causing the first LO to be directed to the first mixer; 
 causing the second LO to be directed to the second mixer; 
 combining outputs of the first transmit channel and the second transmit channel are combined while the first digital signal generator and/or the second digital signal generator are deactivated and further while the first LO is directed to the first mixer and the second LO is directed to the second mixer; and 
 measuring the combined output of the first transmit channel and the second transmit channel. 
 
 
     
     
       2. The radar system of  claim 1  being a synthetic aperture radar (SAR) system that is coupled to an aerial vehicle. 
     
     
       3. A radar system configured to emit a very high instantaneous bandwidth radar signal, where the radar signal has a frequency band, the radar system comprising:
 a first transmit channel, where the first transmit channel comprises a first mixer configured to output a first analog radio frequency (RF) signal having a first RF band based upon:
 a first local oscillator (LO) adapted to generate a LO first frequency; and 
 a first digital signal generated by at least one digital signal generator; and 
 
 a second transmit channel, where the second transmit channel comprises a second mixer that outputs a second analog RF signal having a second RF band based upon:
 a second LO adapted to generate a second LO frequency different from the first LO frequency; and 
 a second digital signal generated by the at least one digital signal generator; 
 
 wherein the at least one digital signal generator is adapted to control the amplitudes and shifts phases of the first digital signal and the second digital signal based upon a computed system LO leakage; 
 wherein the amplitudes and phases of the first digital signal and the second digital signal are shifted to address leakage of the first LO and the second LO across transmit channels of the radar system; 
 wherein the radar signal is based upon the first analog RF signal and the second analog RF signal, wherein the frequency band of the radar signal includes the first RF band and the second RF band; 
 wherein the first RF band and the second RF band partially overlap; 
 wherein the at least one digital signal generator is adapted to generate the first digital signal and the second digital signal based upon a computed correction signal; and 
 wherein the computed correction signal is configured to address variance in magnitude in the radar signal where the first RF band and the second RF band partially overlap. 
 
     
     
       4. The radar system of  claim 1 ,
 wherein the first transmit channel includes a first antenna that is operably coupled to the first mixer; 
 wherein the second transmit channel includes a second antenna that is operably coupled to the second mixer; and 
 wherein the first antenna is adapted to radiate the first analog RF signal and the second antenna is adapted to radiate the second analog RF signal to form the radar signal. 
 
     
     
       5. The radar system of  claim 1 , further comprising:
 a combiner that is operably coupled to the first mixer and the second mixer, wherein the combiner is adapted to combine the first analog RF signal and the second analog RF signal to form the radar signal; and 
 an antenna that is operably coupled to the combiner, wherein the antenna is adapted to radiate the radar signal. 
 
     
     
       6. A radar system configured to emit a very high instantaneous bandwidth radar signal, where the radar signal has a frequency band, the radar system comprising:
 a first transmit channel, where the first transmit channel comprises a first feedforward loop, and a first mixer configured to output a first analog radio frequency (RF) signal having a first RF band based upon:
 a first local oscillator (LO) adapted to generate a LO first frequency; and 
 a first digital signal generated by at least one digital signal generator; and 
 
 a second transmit channel, where the second transmit channel comprises a second feedforward loop, and a second mixer that outputs a second analog RF signal having a second RF band based upon:
 a second LO adapted to generate a second LO frequency different from the first LO frequency; and 
 a second digital signal generated by the at least one digital signal generator; 
 
 wherein the at least one digital signal generator is adapted to control the amplitudes and shifts phases of the first digital signal and the second digital signal based upon a computed system LO leakage; 
 wherein the amplitudes and phases of the first digital signal and the second digital signal are shifted to address leakage of the first LO and the second LO across transmit channels of the radar system; and 
 wherein the radar signal is based upon an output of the first feedforward loop and an output of the second feedforward loop and upon the first analog RF signal and the second analog RF signal, the frequency band of the radar signal including the first RF band and the second RF band. 
 
     
     
       7. The radar system of  claim 6 ,
 wherein the first feedforward loop includes a first attenuator and a first phase shifter; 
 wherein the first LO is provided as input to the first feedforward loop, attenuated by the first attenuator, and phase-shifted by the first phase shifter; 
 further wherein the output of the first feedforward loop is combined with the first RF signal; and 
 wherein the second feedforward loop includes a second attenuator and a second phase shifter; 
 wherein the second LO is provided as input to the second feedforward loop, attenuated by the second attenuator, and phase-shifted by the second phase shifter; 
 further wherein the output of the second feedforward loop is combined with the second RF signal. 
 
     
     
       8. The radar system of  claim 7 , wherein a first amount of phase-shifting performed by the first phase-shifter and a second amount of phase-shifting performed by the second phase shifter is performed based upon the computed system LO leakage. 
     
     
       9. The radar system of  claim 3  being a synthetic aperture radar (SAR) system that is coupled to an aerial vehicle. 
     
     
       10. The radar system of  claim 6  being a synthetic aperture radar (SAR) system that is coupled to an aerial vehicle. 
     
     
       11. The radar system of  claim 3 ,
 wherein the first transmit channel includes a first antenna that is operably coupled to the first mixer; 
 wherein the second transmit channel includes a second antenna that is operably coupled to the second mixer; and 
 wherein the first antenna is adapted to radiate the first analog RF signal and the second antenna is adapted to radiate the second analog RF signal to form the radar signal. 
 
     
     
       12. The radar system of  claim 6 ,
 wherein the first transmit channel includes a first antenna that is operably coupled to the first mixer; 
 wherein the second transmit channel includes a second antenna that is operably coupled to the second mixer; and 
 wherein the first antenna is adapted to radiate the first analog RF signal and the second antenna is adapted to radiate the second analog RF signal to form the radar signal. 
 
     
     
       13. The radar system of  claim 3 , further comprising:
 a combiner that is operably coupled to the first mixer and the second mixer, wherein the combiner is adapted to combine the first analog RF signal and the second analog RF signal to form the radar signal; and 
 an antenna that is operably coupled to the combiner, wherein the antenna is adapted to radiate the radar signal. 
 
     
     
       14. The radar system of  claim 6 , further comprising:
 a combiner that is operably coupled to the first mixer and the second mixer, wherein the combiner is adapted to combine the first analog RF signal and the second analog RF signal to form the radar signal; and 
 an antenna that is operably coupled to the combiner, wherein the antenna is adapted to radiate the radar signal.